This invention is directed to prosthetic dentistry.
Many people require repair or removal of teeth and the bridging of teeth. There is employed dental appliances such as jackets, crowns, inlays, onlays, bridges and combinations of these. To assist the dental technician in making the dental appliances there is often prepared a dental model of the mouth and teeth of an individual. The dental model may be of both the upper teeth and the lower teeth or the upper jaw and the lower jaw or the teeth and the lower jaw or the teeth and the upper jaw.
In the preparation of the dental models there is formed a NEGATIVE of the jaw or jaws of the individual. A yieldable material which will retain its shape and configuration after the individual bites into the yieldable material is used. The yieldable material may be a plastic or a rubber or a similar flexible material. The individual bites into this yieldable material and leaves recesses corresponding to the teeth and the gums.
For example, assume that an individual in the jaw has a full set of teeth but that one tooth needs a cap or a crown. The individual bites into the yieldable material to leave the impression of all the teeth and the jaw. The recess in the yieldable material will be more shallow for the stub of the tooth needing the crown or cap.
After the NEGATIVE has been formed in the yieldable material then a pourable dental casting stone is poured into the NEGATIVE. In time, say thirty (30) minutes to sixty (60) minutes, the pourable dental casting stone cures and hardens into the dental mold. The dental mold is removed from the NEGATIVE.
Then, the dental stone in the form of the stub of the tooth is isolated. The isolated dental stone in the configuration in the stub of the tooth is then used for preparing the cap or crown.
Over the years a number of techniques have been developed for making the dental model and also the dental stone model of the stub of the tooth. One technique is the Thompson method. In the Thompson method, in order to accomplish the removal of the dental stone replica of the stub of the tooth, two separate pourings of dental stone were poured into the NEGATIVE or the impression of the teeth and gum of the individual. It was necessary to have a separating material or a parting material between these two pourings of the dental stone. The Thompson technique often produced undesirable results because it failed to overcome the difficulty of initially freeing and separating the segment from the master model after the master model was hardened and removed from the NEGATIVE or impression of the teeth and gum. Also, the Thompson technique was time consuming and expensive.
One of the problems associated with the dental stone replica of the stub of the tooth is to position the dental stone replica into the dental stone model. The dental stone replica of the stub of the tooth can be removed from the dental model and then replaced. It is necessary to have an exact alignment of the dental stone replica of the stub of the tooth in the dental stone model so as to have a good and proper fit of the cap of the tooth. A patent to M. W. Kelly, U.S. Pat. No. 3,470,614, issuing date of Oct. 7, 1969 teaches of a method and an apparatus for making a dental model and also for positioning a protuberance 20 in the NEGATIVE and then a dowel pin 30 and a keying portion 40 on the dowel pin 30 in the NEGATIVE or the impression of the teeth and gum of an individual. A pourable dental casting stone is poured into the NEGATIVE and surrounds the dowel unit 30 and the keying portion 40. In time, the dental mold is removed from the NEGATIVE and the keying portion 40 and the dowel pin 30 are isolated and removed from the dental mold. The stub of the tooth surrounds the keying portion 40 and the dowel unit 30. The keying portion 40 of Kelly is wedged or firmly positioned in the NEGATIVE or in the impression of the teeth and gum of the individual.
A patent to Angelo C. Tirino, U.S. Pat. No. 4,238,189, issuing date of Dec. 9, 1980 teaches of positioning a divider and a pin in the NEGATIVE. The pourable dental casting stone is poured into the NEGATIVE and surrounds the divider and also the pin. After the casting stone has cured into the dental model the stub of the tooth can be isolated and separated from the dental model to assist in preparing the crown or cap.
There are two patents to Ronald E. Huffman, U.S. Pat. No. 3,937,773 issuing date of Feb. 10, 1976 and also U.S. Pat. No. 4,398,884 issuing date of Aug. 16, 1983. These patents teach of positioning a retainer in the NEGATIVE and making two dental pours. The retainer has recesses or passageways for receiving an aligning pin. Then, the second pour can be made around the upper part of the aligning pin. After the dental stone has cured and hardened the stub of the tooth can be isolated for further work in preparing the crown or cap.
The foregoing comments with respect to isolating and separating the stub of the tooth for use in preparing a crown or a cap is also applicable in regard to preparing a bridge, a jacket and the like.